Path: utzoo!mnetor!uunet!husc6!cmcl2!beta!unm-la!unmvax!nmtsun!hydrovax
From: hydrovax@nmtsun.nmt.edu (M. Warner Losh)
Newsgroups: comp.lang.fortran
Subject: Re: Modifying iteration variables in DO loops
Message-ID: <1328@nmtsun.nmt.edu>
Date: 3 Feb 88 03:41:16 GMT
References: <1309@nmtsun.nmt.edu>
Organization: NMT Hydrology program
Lines: 48
Keywords: X3 standard FORTRAN 77
Summary: WRONG or RTFM

In article <1309@nmtsun.nmt.edu>, john@nmtsun.nmt.edu (John Shipman) writes:
> In section 11.10 of X3.9-1978, the FORTRAN 77 standard (pp. 11-5 to
> 11-9), there is no statement about prohibiting the modification of a
> DO variable within a loop.  The standard defines how this works for
WRONG.

11.10.5 (pg 11-8) EXECUTION OF THE RANGE.  Statements in the range of
a DO-loop are executed until the terminal statement is reached.
Except by the incrementation described in 11.10.7, the DO-variable of the
DO-loop may be neither redefined nor become undefined during the execution
of the range of the DO-loop.

So, in other words, the redefinition of a loop variable is prohibited inside
the range of a loop.  You can't assign a value to a loop variable, that,
according to the standard, is a redefinition of the loop variable.

> 
> For example, with some mythical standard-conforming compiler, this loop
> would be executed twice, and the final value of COUNT would be 5:
> 
>            do 86 count = 1, 2
>              count = count + 1
>       86   continue
> 

WRONG WRONG WRONG WRONG WRONG WRONG WRONG

There is NO CORRECT answer here, since this isn't a standard following
program.  According to section 13.10.5 sighted above, the assignment
to count is NOT ALLOWED IN A STANDARD CONFORMING PROGRAM.

> I bet NOBODY has a standard-conforming compiler. 

WRONG.  Since this is a not a F77 program, you can't feed it to a F77
compiler and say that the compiler is broken.

As a side note : On VMS, the FORTRAN compile gives a warning message telling
me that I was modifying a loop variable.

One final thing, when you quote some text, please make sure that you
have read the supporting text around it before using the quotation
out of context.

-- 
bitnet:	losh@nmt.csnet			M. Warner Losh
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